Optimization of total resolved shear stress in AlN single crystals homoepitaxially grown by physical vapor transport method

We investigate the distribution and evolution of the total resolved shear stress (TRSS) in AlN single crystals homoepitaxially grown by the physical vapor transport method based on an in-house three-dimensional thermalelastic stress code. The thermal stresses of three primary slip systems in 2H-AlN crystals are modeled. The simulation results show that the magnitude of the TRSS increases tremendously after the crystal reaches its critical thickness delta(c) at 6 mm under our specific hotzone and growth conditions. The location of the maximum TRSS transitions from the bottom surface of the crystal to the peripheral region beneath the seed crystal during the growing process. The influences of the power ratio between two resistant heaters on the TRSS and the growth rate are also investigated. The results suggest that a high growth rate could be maintained until the crystal thickness reaches delta(c) and that the temperature gradient inside the growth chamber should be decreased during the later stages by adjusting the power ratio to reduce the overall TRSS and defect propagation. The TRSS could be reduced by 93.31% by rapidly decreasing the temperature differences in AlN crystals immediately after the growth process.